Like so many people here, I knew I wanted to be in nappies almost as soon as I was out of them. When I was much younger, I did share this "secret" with one or two of my friends, and one of them seemed interested too, though I think he was curious just because I talked about it quite a lot.
Despite that, as I got older and my feeling only intensified, I was convinced that my friend would have grown out of such a childish interested and that I was the only person that felt this way about nappies. I felt like a complete freak, and entirely alone in the world. That aspect of it certainly didn't do very much for self-esteem.
I can't remember exactly how old I was when I first got an inkling that other people out there might like nappies too, but I guess I would have been around 14. I'm also not sure exactly what first made me aware of it, but there are two possible candidates, I'm just not sure which came first.
I remember that my older brother had a stash of "adult magazines" and I knew where he hid them. I recall that they featured a lot of adverts for 'phone line services, and every now and then adult baby story lines were advertised. In the days before itemised billing, I 'phoned them once or twice. They weren't great, but it was reassuring to see them advertised in "mainstream" top-shelf magazines.
As
@RubberJin mentioned, there was an episode of 90s TV programme "Eurotrash" that featured adult babies. I think this might predate my exposure to my brother's reading material, but even if it didn't, it was the real confirmation that there were others who really did want to be treated like babies. Even more than that, it showed a world where that might even be possible. I'd certainly say this was the thing that had the biggest impact on me. Although everything on Eurotrash was presented as a joke, it has a powerful impact on me.
Although this was definitely after seeing Eurotrash, I can vividly remember when I was first made aware of "baby sitting" services. When I was 15, I went to London with family and I was allowed some time on my own to explore. My Dad had a mobile 'phone, and I had to call him to check-in with him after a few hours. It was in the days before mobiles were all that common, so I had to use a payphone. London 'phone boxes used to be plastered with cards featuring adverts for prostitutes and dominatrixes, and I saw one offering services for adult babies. I just couldn't believe it! The fact that they'd bothered to print up a card advertising this service meant that there must be more of us than I had previously realised. I still knew that it was unusual, but at least it wasn't just me.
The internet came a little bit later, but, again in common with a lot of people here, much of what I found was creepy and off-putting. Just one of the many reasons why I'm so glad I found this forum!